Grinding machine

ABSTRACT

A grinding machine wherein the griding wheel is moved relative to the workpiece by a screw rotated by an electric motor that produces a torque that is proportional to the current applied thereto. The movement of the grinding wheel is controlled in an improved constant force mode or an improved constant rate mode or in an improved combination of both modes.

[ 1 June 25, 1974 United States Patent Seidel 3 698,138 10/1972 Wada et51/165 8 3,716,949 2/1973 Price et 51/165.8

[ 1 GRINDING MACHINE [75] Inventor:

William B. Seidel, Birmingham, Mich.

Assignee: The Babcock & Wilcox Company,

Primary Examiner-Harold D. Whitehead Attorney, Agent, or FirmBarns,Kisselle, Raisch & Choate [22] Filed:

[57] ABSTRACT A grinding machine wherein the griding wheel is [52] US.5l/l65.8, 5 l/l65.87 moved relative to the workpiece y a Screw rotated y[51 im. B24b 49/16 an electric motor that produces a torque that is p[58] Field 61 Search.......... 51/165 R, 165.8, 165.81, Portional to thecurrent pp thereto The movement of the grinding wheel is contro11ed inan improved constant force mode or an improved constant rate mode or inan improved combination of both modes.

3,085,371 Lessman.................... 51/165.8 71 Claims, 13 DrawingFigures PAIENTEDJUNZS m4 SHEET 2 BF 8 FIG 3 F'IG.Z

PATENIEUJUNZSIBH SHEET b 0F 8 iii . Nmw Qm x o E MIN qm T T E GRINDINGMACHINE This invention relates to grinding machines and particularly toa method and apparatus for producing precise relative movement between aworkpiece and a machine tool such as a grinding wheel.

BACKGROUND OF THE INVENTION In machines such as grinding machines, it isconventional to rotatably support a workpiece in a appropriate mannerand cause relative movement between the rotating workpiece and arotating grinding wheel to produce accurate surfaces on the workpiece.

Two types of feed systems are commonly used commercially for causingrelative movement between the workpiece and the grinding wheel and theyare commonly referred to as fixed rate and force feed systems.

In the fixed rate feed system, the grinding wheel is moved a specificradial distance, typically a fraction of a thousandth to a fewthousandths of an inch, for each rotation of the workpiece. Variousmeans have been used for producing the fixed feed rate. One commonmethod is to drive the support for the grinding wheel by means of ascrew which itself is driven by a stepping motor. The fixed feed rate isthen determined by controlling the number of stepping pulses in relationto the revolutions perunit time of the workpiece.

In the force feed system, the grinding wheel is moved with respect tothe workpiece with a constant force. One common type force feed systemcomprises the use of a hydraulic actuator for moving the support orslide for the grinding wheel. The pressure supplied to the hydraulicactuator is maintained at a constant predetermined value by anappropriate pressure control device resulting in a constant forceexerted on the support for the gringing wheel. The constant forceexerted by the hydraulic actuator does not always insure constant forceof the grinding wheel against the workpiece because of the friction thatis involved in moving the support. Accordingly, various low frictiondevices have been used such as hydrostatic slides and the like to reducethe friction.

Although fixed rate feed systems have received wide acceptance and areoften satisfactory, there are certain disadvantages in presentcommercially available fixed rate feed systems. One disadvantage is thatsince the hardness of successive parts or workpieces in a production runmay differ, the optimum feed rate is greater for softer than for hardermaterial. Thus, it may be that the wheel is driven at a rate faster thanthe optimum because of the variation in hardness of the workpieces. Ithas been conventional to adjust the feed rate for the hardest materialanticipated. As a result, the softer workpieces are ground at a slowerrate than optimum with a consequent waste of time and possible reductionin the quality of the grinding operation. Another disadvantage of aconstant or fixed feed rate system is that some additional system mustbe provided for rapid traverse of the grinding wheel up to the pointwhere the wheel first makes contact with the workpiece. Otherwise, thereis a substantial loss in time. If the workpieces vary in size, the feedrate must be established at a nominal size to accommodate the largestworkpieces resulting in a loss of valuable time due to the relativelyslow movement at the constant feed rate before any actual contact withthe workpiece occurs.

Experience has indicated that if the range of hardness variessubstantially, optimum feed rate can be achieved by using aconstantforce feed system. The use of such a constant force feed system resultsin a feed rate which will be slower for harder material and faster forsofter material. If the preset force is accurately established byexperience, the feed rate will be substantially optimum for a practicalrange of hardnesses. Thiswill result in high production because thesofter pieces are cut faster and the harder pieces are produced at aslower rate with acceptable finish quality. Furthermore, by utilizing aconstant feed force, workpieces of varying initial diameters or sizescan be accommodated by a deceleration from the traverse rate to anominal feed rate. The nominal feed rate can be set somewhat higher thanthe highest feed rate to be used in actual cutting. Thus, the grindingwheel can be advanced more rapidly until contact with the workpiece isestablished. Then, the constant force feed rate automatically reducesthe feed rate to the optimum for the hardness of the workpice beingworked upon. However, there is a problem with respect to constan forcefeed systems in that if a workpiece is eccentric, the high side of theworkpiece tends to push the grinding wheel back against the constantforce due to the high compliance of the hydraulic system used. The pushback of the grinding wheel merely diverts more fluid through thepressure control device while still maintaining constant force and thegrinding wheel continues to cut all around the workpiece to the desireddepth per turn but does not clean up the eccentricity.

Thus, in one type of system that has heretofore been proposed, aconstant force feed is established by a hydrualic actuator or the likeuntil the final finish grinding during which a stepper motor is utilizedto produce a constant rate feed in an effort to remove the eccentricity.

One of the problems with respect to the use of a stepper motor in bothconstant rate feed and constant force feed is that the rate of pulsetransmission is depended upon to establish the rate of grinding wheelmovement and the number of pulses transmitted is counted and is utilizedto determine the distance traveled. However, fluctuations in loading canresult in overloading of the stepper motor so that some or all of thepulses fail to produce the intended motion. In such cases, either orboth the distance and the rate may be different from that which wasintended.

Another problem with respect to prior grinding machines relates to themanner of determining when the grinding wheel should be dressed. Onemethod that has been suggested is to sense the actual wear of the wheeland then dress the wheel when the wear exceeds a predetermined amount.Another method comprises dressing the wheel after a predetermined numberof cycles. The proper and timely dressing of the wheel is particularlyimportant in connection with constant force grinding systems since adull wheel will result in inefficient grinding from the standpoint oftime and surface finish.

Another problem with respect to prior grinding machines relates to speedof rotation of the workpiece. conventionally, the operator mustcalculate the desired speed of rotation from the diameter of theworkpiece and the desired surface speed (S.F.M.). This necessitates aseparate calculation for each diameter and surface speed to be used.

Accordingly, among the objects of the invention are to provide agrinding machine wherein relative movement between the workpiece and thegrinding wheel can be produced either at a fixed rate, at a constantforce feed, or any desired combination of both; wherein in either mode,the eccentricity of the workpiece is removed; wherein the movement inthe force feed mode is controlled to remove eccentricity; wherein bothrapid traverse and extremely slow feed rates are achieved by a singleprime mover; wherein the disadvantages of the use of a stepper motor areavoided; wherein a signal for wheel dressing and wheel wear is producedwithout calculation on the part of the machine operator; wherein themovement of the grinding wheel relative to the workpiece is maximized interms of time so that the optimum time is involved; wherein the machineaccommodates for diameter of the workpiece and desired cutting speedwithout calculation by the operator.

SUMMARY OF THE INVENTION A grinding machine wherein the grinding wheelis moved relative to the workpiece by a screw that is rotated by anelectric motor that produces a torque that is proportional to thecurrent applied thereto. The movement of the grinding wheel iscontrolled in a constant force or a constant rate mode.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective view of agrinding machine embodying the invention.

FIG. 2 is a side elevational view of a grinding machine embodying theinvention.

FIG. 3 is a fragmentary sectional view taken along the line 3--3 in FIG.2.

FIG. 4 is a graph to the torque-current characteristic of a motorutilized in the machine.

FIG. 5 is a graph of the torque-current characteristic as modified foruse in the machine.

FIG. 6 is a cycle chart forone mode of operation.

FIG. 7 is a cycle chart for another mode of operation.

FIG. 8 is a plan view of a control panel utilized in the machine.

FIG. 9 is a time chart of R.P.M. and motor current during the operationof the machine.

FIG. 10 is a schamatic of a portion of the electronic circuitry.

FIG. 11 is a schematic of another portion of the elec- 'troniccircuitry.

FIGS. 12A and 12B are portions of a schematic of another portion of theelectronic circuitry.

DESCRIPTION Referring to FIGS. 1-3, the invention is shown as applied toa grinding machine comprising a base 10 with a table 11 thereon on whicha workpiece W is rotatably supported by an appropriate mandrel l2 androtated by a motor 13. The table 11 may be reciprocated by appropriatemechanism (not shown). The machine further comprises a main slide 14 anda cross slide 15 on which a grinding wheel G is rotatably mounted anddriven by a motor 16.

The main slide 14 is supported on the base 10 by hydrostatic bearingssuch as disclosed in the US. Pat. to

Porath No. 3,231,319, issued Jan. 25, I966. The cross slide 15 is, inturn, supported on the main slide 14 by similar hydrostatic bearings.Slide 14 can be reciprocated on base 10 by a suitable mechanism (notshown).

A screw 20 is rotatably mounted by ball bearings 21 on the main slide14. A nut 22 of the ball bearing type is mounted on the screw 20 andconnected to the cross slide 15 by integral flanges 23. Torque forturning the screw 20 is provided at one or both ends by electric motors25 of the precision torque type. More specifcally, the available torquefrom a motor of this type is accurately proportional to the value ofcurrent flowing in its windings at any given time, as shown in thegraph, FIG. 4. Such motors are usually provided with permanent magneticfields and are adapted to be energized by direct current. Thus, byadjustment of the current in the motors 25, the torque applied to thescrew 20 may be accurately controlled.

If the screw were rotated without friction in its end bearings and inthe nut, the torque produced by the motors would be convertible withoutloss of proportional force on the cross slide 15. In such case, thefrictionless screw drive would be reversible, that is, reactive force onthe slide would, if sufficient, cause reverse rotation of the motors. Insuch an arrangement, an eccentric workpiece could be ground at constantfeed force but with no correction of the eccentricity.

In accordance with the invention, the bearings 21 supporting the ends ofthe screw 20 are deliberately preloaded to provide a carefullycontrolled constant frictional resistance to rotation of the screw 20.This frictional resistance is adjusted to a value just above thethreshold of reversibility so that the friction is high enough toprevent rotation of the screw 20 by a force on the cross slide 15. Anyconventional means can be used for preloading the bearings 21.

Further, in accordance with the invention, a constant minimumforward-driving current is provided for the motors 25 such that theconstant screw friction is equalized. Then, by adding a forward-drivingcurrent, a proportional force is provided for the slide 15. This isshown in the graph in FIG. 4. By this arrangement, the constant frictionload on the screw is overcome by the constant minimum forward-drivingcurrent and any additional forward-driving current produces the desiredproportional force of the slide 15.

For example, a deliberately provided friction of 1 lb.- ft. can beprovided on the screw 20. A constant basic current in each of the motorsmay be 4 amperes which is sufficient to produce I lb.-ft. torque. Eachadditional ampere to the two motors produces a total of 0.25 lb.- ft. oftorque. With a fixed or tare friction cancelled out by the constantbasic 4 amperes, any additional current produces proportional torquewhich is transmitted to the table. As indicated above, the hydrostaticconstruction of the slide and table produces as essentially frictionlessrelationship which will not impede movement of the grinding wheel by themotors.

Further, in accordance with the invention, an encoder or pulse generator26 is provided on the end of the screw 20. The encoder 26 includes ahousing fixed to slide 14 and a rotatable member fixed to screw 20. Atypical encoder comprises a pulse generator of the optical-electronictype having a very high resolution on the order of 20,000 pulses perrevolution of the .shaft. Thus, in a screw having a thread lead of 0.2inch per revolution, a travel of 0.000010 inch can be obtained for eachpulse generated.

This relationship can be summarized as follows:

Feed screw lead 0.200 inch One revolution equals 20,000 pulses One pulseequals 0.000010 inch As presentlydescribed, by means of electronicelements including a high speed counter, the pulses from the generator26 can be totaled over a period and used to'record distance of slidetravel. Other electronic elements perform a differentiation with respectto time which delivers a signal representing the rate of pulses persecond from the generator. Pulses per second can be scaled by theelectronic circuitry to represent inches per minute (or per second) ofslide travel rate. Thus, using the pulse generator 26 and its associatedelectronic circuitry, it is possible to have available signalsrepresenting the position of the slide and the rate of motion of theslide 15.

These rate and position signals can be used not only for indication butalso for control. In the case of position, a predetermined pulse countvalue can be entered at the start of a segment or portion of slidemotion. When a pulse count has been accumulated from the encoder 26 thatmatches the preset value, the segment of motion will be terminated bystopping or changing speed of the drive motors. Likewise, speed of slidemotion may be controlled by presetting a signal representing the desiredspeed. This signal is compared with the pulse rate from the encoder 26and the voltage to the motors is automatically adjusted until the pulserate matches the preset value.

It is to be noted that the available torque produced by a DC. motor isdetermined by the value of current flowing (as previously mentioned)while the speed of the motor is controlled by the voltage applied. As iswell known, these two quantities are interrelated and they cannot bothbe independently controlled at the same time. However, either can beregulated to suit a condition and the'other will automatically assume aconsistent value. In the following description, there will be situationsin which the torque value is significant. In such cases, the currentflow is controlled while the voltage and speed conform. In othersituations, speed control is paramount. In those cases, the voltage iscontrolled while the current and torque conform.

The use of the above design for both position and speed make theapparatus embodying the invention exceptionally versatile and positive.Using the feed-back encoder or pulse generator assures that only actualmotion of the screw produces pulses which are interpreted for speed anddistance.

A typical pulse generator is of the type manufactured by BaldwinElectronics Inc., Little Rock, Ark., and designated Model 5V671D OpticalIncrement Encoder with a maximum frequency response of outputs 200 KHz.

The modes or manners in which the apparatus embodying the invention canbe used are shown in the cycle charts, FIGS. 6 and 7. As shown in FIG.6, the fixed feed rate mode comprises an overall range with a rapidtraverse range that can be varied. Within the rapid traverse range,there is a total feed for grinding. Just prior to the beginning of thetotal feed, there is a deceleration. Upon contact with the workpiece,the total feed is initiated. The total feed, in turn, is divided into afast feed that can be varied both in rate and length, a medium feed thatcan be varied both in rate and length, and a finish feed that can bevaried both in rate or length.

The grinding machine can also be operated in a different mode analogousto a constant force feed but since it has definite advantages overconventional constant force feed, it is herein designated as a feedpaper mode. As shown in FIG. 7, in the feed pacer mode, there is anoverall range, a variable rapid traverse range, and a total feed rangedivided into a fast feed and finish feed of variable force and lengthand variable rate and length within the total feed range. As in the caseof the fixed feed rate, there is a deceleration and upon contact withthe workpiece, the fast feed is initiated. In addition, as presentlydescribed, there is a dull wheel sensing which occurs just prior to thefinish feed.

Also, in both modes, the optimum workpiece rate of rotation is alwaysutilized.

A control panel for the grinding machine is shown in FIG. 8 andcomprises a plurality of push button switches having the followingdesignations:

WORKHEAD CONTINUOUS WORKHEAD AUTO SLIDE RETRACT DRESS CYCLE SINGLE CYCLESTART AUTO STOP

LOAD

UNLOAD CHUCK DE-CHUCK FEED PACER (Fp) FIXED FEED (F MINUS In addition,the panel includes thumb wheel switches for the following selections:

RETRACT LENGTH TOTAL FEED LENGTH MEDIUM FEED LENGTH FINISH FEED LENGTHFEED RATE FEED FORCE MEDIUM FEED RATE FINISH FEED RATE DRESSAMOUNT/PASSES DRESS CYCLE COUNT WHEEL SENSOR TIME/INCREASE DWELLREVOLUTIONS SLIDE RANGE SIZE COMPENSATOR WORK S.F.M.

WORK DIAMETER In both charts, FIGS. 6 and 7, the zero position at theright represents the position of the grinding wheel when it is fulladvanced and its cutting operation is completed. Thus, all otherpositions on the charts are reckoned back from final finish depth. Itmay be noted that positions marked on the charts are not scaled to bepictorially representative of actual relative locations.

In both charts, the full length is designated range and is indicated asl0 inches long, as an example. The range is the full travel capacity ofthe feed slide screw. This provides, amon other things, for changingwheels, maintenance work, etc.

In both charts, the distance from zero to the start of rapid traverse isgiven as 4 inches, for example. This distance can be less than themaximum, as more fully described below.

The start point for rapid traverse is the normal parking location forthe wheel slide between workpieces and allows clearance for loadingpieces, manual gauging, etc. Rapid traverse itself is forward slidemotion at a speed many times greater than any feed rate. This speed isautomatically controlled by a factory-set signal which is compared withthe generated pulse rate, as aforesaid. The purpose of rapid traverse isto move the wheel quickly from the parking position to a position justbefore contact with the work.

The distance marked total feed in both charts is the distance from zeroto (or just outside of) first contact with the work. This distancedepends upon the total amount of the stock to be removed from theworkpiece and is determinedby the machine operator who sets in theamount by means of the digital thumbwheel switch designated 100 in FIG.8.

The distance from the start of rapid traverse is controlled by countingpulses from the start of rapid traverse to the preset start of totalfeed length. This is an automatic function of the electronic circuitry.

As indicated on both charts, the slow down from rapid traverse to feedrate occurs over a distance of 0.100 inch preceding the start of thetotal feed segment. The distance from start of rapid traverse to thestart of the deceleration interval is controlled by pulse count. Theposition for the start of deceleration is always 0. 100 inch ahead ofthe start of total feed and is automatically shifted by the setting ofswitch 100.

As presently described, the electronic control circuitry includeselements which use accumulated pulse counts conjointly with the pulserate to change the desired pulse rate progressively during the slowdown.

Fast feed is an interval within the total feed interval. In the fixedrate chart of FIG. 6, it extends to the start of medium feed. Duringthis interval, the wheel advances at fixed feed rate using the pulserate from generator 26 as the control signal, as previously explained.The criterion for this feed rate is set by the operator by means ofthumbwheel switch 102 shown in FIG. 8. The distance traveled at fastfeed is determined by pulse count up to the accumulated total set by theoperator on switch 104 as the start of medium feed. The medium feedinterval extends to the start finish feed and terminates when the pulsecount matches that set on switch 106 (FIG. 8).

The fast feed for the pacer mode of FIG. 7 is executed under theconditions for force feed as explained previously herein. However, themaximum feed rate during this interval is controlled by the pulse rateand the criterion is set on switch 102 (FIG. 8) just as was the fastfixed rate referred to in FIG. 6. The difference is that the setting ofswitch 102 is an actual fixed feed rate for the fixed feed mode of FIG.6 while it is merely a maximum force for the pacer feed mode of FIG. 7.The actual feed rate for the feed pacer mode (FIG. 7) is set by thecurrent in motor(s) 25 and depends upon the hardness of the materialbeing ground. The term pacer rate means that the slide is prevented fromlunging ahead due to gaps or eccentricities.

Obviously, it is necessary to furnish a control signal to determinewhether the control during fast feed is to be at a fixed rate(controlled by pulse rate) or at a rate determined by hardness(controlled by motor current and limited only by pulse rate). Thisselection signal is provided by the push button switches 107 and 108. Ifswitch 107 is pressed, the feed pacer mode is selected and the feed rateis determined by work hardness. If switch 108 is pressed, the fixed ratemode is selected and the feed rate is controlled strictly by pulsecount.

In the fixed rate mode of grinding, it is conventional to start thegrinding at a relatively high feed rate and then reduce it forimprovement of surface finish and other reasons. FIG. 6 shows a mediumfeed interval defined, by accumulation of pulse counts, between thestart of medium feed and the start of finish feed. The feed rate in thisinterval is controlled by pulse rate and the criterion is set on switch110. No medium feed interval is shown on FIG. 7 because the force feedprinciple is used for the whole grinding operation except for the finishfeed, as described below. Thus, in the feed pacer mode, the setting ofswitches 104, 110 is not effective.

It is known that highest accuracy of roundness and the best surfacefinish require that the very last thin layer (fraction of a thousandthof an inch) be removed using a very low fixed feed rate. Thus, thefinish feed interval in both the fixed feed mode and the feed pacer modeis executed at a fixed feed rate. The rate is controlled by pulse rateand the distance by pulse count. The distance is set on switch 106 andthe rate on switch 112. Either mode of operation uses these settings.

As previously described, the feed rate under force or pacer feed isbasically determined by the hardness of the workpiece. However, it is anecessary corrolary that this rate is also affected by the sharpness(presence of fresh particles and lack of glaze) of the wheel. For agiven hardness of work, a sharp wheel will feed faster than a dull wheelunder fixed force.

Assuming a relatively small span of hardness from piece to piece (or arandom mix of hardness from piece to piece), progressive reduction offeed rate, under fixed force, will occur as the wheel becomes duller dueto use. In the feed pacer mode, the time for a predetermined movement ofthe grinding wheel at a portion of the cycle is compared with apredetermined time an a dressing signal is produced when the currenttime exceeds the predetermined setting. More specifically, the operatorinserts a percentage in switch 114 which is representative of therelationship between the time of travel over a specific distance for anewly dressed wheel versus one that required dressing. In the circuitry,the pulses produced by encoder 26 during the 0.001 inch just before thestarting point of the finish feed interval are counted and the time forthat set of pulses is determined in micro-seconds and this time isvisually recorded on the dial of switch 114 for each piece ground. Fromthese two values, the current rate of feed is determined. This currentfeed rate is automatically compared with a previously determined rate interms of good pieces and economical production rate. A certainpercentage decrease in feed rate, due to wheel dulling, is dialed in onswitch 114. When this change is reached, the piece in process isfinished but an automatic dressing operation is initiated to sharpen thewheel before the next piece is ground.

When the pulse count indicates that the wheel has progressed to thepoint marked zero in either chart, the proper size has been reached. Itis necessary, however, to hold that position for a predetermined numberof work revolutions to assure a clean finish. This hold or dwell time,in seconds, will vary according to the diameter and speed of revolutionof the work. It has heretofore been common for the operator to calculatea dwell time based upon diameter of the workpiece and surface speed perminute and to make a time setting in the machine. In accordance withthis invention, the operator sets switch 134 to the desired dwellrevolutions and the electronic circuitry will automatically determineand control the dwell for the desired number of revolutions, taking intoconsideration the diameter and surface speed settings of switches 116,118.

Upon completion of the dwell, in either mode, a signal is given toreverse the motor(s) 25 at rapid traverse rate. The slide retracts toits parking posiion. The distance to the parking position is controlledby pulse count. As before mentioned, the distance to parking position isshown as 4 inches in the example. However, a different retractiondistance can be preset on switch 120.

Machine Set-Up Returning to FIGS. 6 and 7, it is recalled that the fullrange of wheel slide travel is 10 inches in the example. The movement ofthe slide outward beyond the starting position for rapid traverse iscontrolled by pushbuttons 122 in (toward zero in FIGS. 6 and 7) and 124for out. The position of the slide throughout its range is indi cated,by way of pulse counting, on the digital readout device 126.

When a new type of workpiece is to be ground, a sample is put in placeand the desired diameter and surface feet per minute are dialed in onthe switches 116 and 118. This causes the sample workpiece to be rotatedat the proper revolutions per minute, as explained above. Also, thevarious distances and rates are dialed in switches 120, 100, 104, 106,102, 110, 112.

Now the grinding wheel is caused to approach the work by pressing thebutton 122. This button causes the wheel to advance faster the furtherin it is pressed. A typical button comprises a slide actuatedpotentiometer that produces a progressively changing voltage and uponbeing fully depressed actuates a micro switch producing a maximumvoltage. Thus, the operator can cause fast approach to the work and thenmanually reduce the speed for set-up grinding.

The sample piece is thus ground under manual control until it cleans up,that is, until all irregularities or eccentricities are removed and atrue cylinder is being ground. At that time, the wheel is manuallywithdrawn (pushbutton 133) to the extent of the setting of retractionlength on switch 120. Next, the part is gauged for diameter. Thisgauging may be manual or, in more advanced embodiments, by automaticgauging devices.

In the original description of FIGS. 6 and 7 above, it was asserted thatthe zero end represents the slide position for a finish piece.Therefore, if the cleaned up sample is found to be of proper diameter,it means that the slide reached (and did not pass) zero position. If thesample is found to be too large (assuming CD.) it means the wheel didnot reach zero position and should go further when a production piece isto be made under automatic control. This is equivalent to moving thezero end of the cycle in FIGS. 6 and 7 to the left. Conversely, if thesample is too small (still O.D.) zero should be moved to the right. Itis clear that moving the zero maintains the relative positions of alldistance points on the charts.

Based on the gauged sample, the operator dials in the error in diameteron the switch 128. He then presses button if the sample is too large(O.D.) or button 132 if it is too small. The effect of pressing buttons130 or 132 is to electrically move the zero of FIGS. 5 and 6 by theamount dialed in on switch 128 so that the zero setting conforms to thezero wheel position at the end of final feed. Thereafter, all the switchsettings on FIG. 8 are properly correlated to the corrected zero andproper size pieces will then be ground. Should diametererrorssubsequently appear, the effective zero can be moved at any time by anew setting of switch 128 and pressing of buttons 130 or 132.

In the early part of this description, feed rate was defined as wheeladvance per revolution of the work.

In prior art machines, the feed rate is basically set in numbers whichare not related to any specific relationship to the workpiece. Therevolution rate of the workpiece is dependent upon its diameter and thecorrect peripheral speed or S.F.M. (surface feed per minute). From thiscalculated revolution rate, a further calculation is necessary todetermine inches per minute of feed rate to get the desired inches perrevolution. All these calculations are normally done manually or, atleast, away from the grinding machine.

As already described, the machine of the invention provides electroniccircuitry to establish the R.P.M. of the work according to dialed indiameter and S.F.M. in switches 11.6, 118. As presently described,further electronic circuitry uses this work R.P.M. together with thevarious dialed in feed rates, in inches per revolution to set the pulserate criteria accordingly.

Referring to FIG. 9, the upper curve represents the variation in R.P.M.of the motor 25 which translates the grinding wheel during variousportions of the cycle. As can be seen, the R.P.M. increases during theacceleration portion after which it remains constant during rapidtraverse. It then decelerates to an intermediate rate during the workdetection portion of the cycle. Upon contact of the work, the R.P.M.remains constant until the finish feed mode or portion of the cycle. Atdwell, the R.P.M. diminishes to zero and then reverses for retraction.Simultaneously, during the various portions of the cycle, the motorcurrent to the motors 25 changes correspondingly as is evident from thelower curve.

Electronic Circuitry Referring to FIG. 10, the digital servo amplifierfor providing a varying voltage to the motor 25 comprises adiscriminator that receives pulse signals from the encoder and also fromthe function generator presently described. The signals from thediscriminator pass to a quadrant detector 151 and, in turn, to anup-down counter 152 to a digital gain select 153 and then to a digitalto analog converter 154. The quadrant detector 151 functions to preventthe excess down pulses which occur during acceleration or decelerationfrom causing instability in the system. Specifically, the detector 151operates to produce a pulse when the down count reaches zero to insurethat the next pulse will be in an up direction. The analog converter 154provides a signal to an amplifier 155 that, in turn, supplies thearmature voltage through line 156 to the motor 25. A servo motor 25driven by the output of the amplifier 155 supplies a reading of armaturecurrent through line 157 for use as presently described. The functioningof the motor 25 to compensate for the preloading of the bearings isachieved by the use of the dead band gain compensator 158. Compensator158 balances out the required torque to turn the screw and the constantforward driving current so that any input signal will cause rotation ofthe screw. Other input and output signals are provided as labeled inFIG. for use as presently described. Following error detection unit 159functions to produce a warning or shout down signal in the event thefollowing error is excessive. Digital gain set functions to provide fordifferent gain in various portions of the cycle. Thus, there may be lowgain to point A, then high gain to retract and then low gain duringretraction. The analog error signal can be used to change the oscillatorand eliminate excess following error.

Referring to FIGS. 12A and 12B, which are schematics of the functiongenerator, the pulses supplied to the discriminator 150 in FIG. 10 arederived from gating 160. The sequencing of the pulses to the gating iscontrolled by a sequence shift register 161 to which the inputs from thevarious thumbwheel switches are provided. For purposes of clarity, theinputs have been designated with the same reference numerals as in thecontrol panel, FIG. 8.

In the constant rate mode, the sensing of work revolutions per unit timeis applied to a digital to analog converter 162 and, in turn, the analogoutput thereof is converted to a proportional pulse rate by a voltagecontrolled oscillator 163. The rate at which the pulses are permitted topass to the gating 160 in each portion of the cycle is controlled by thesetting of the switches 102, 110, 112 and the duration thereof iscontrolled by the setting of the switches 100, 104, 106. Thus, the speedand distance of the grinding wheel movement toward the workpiece iscontrolled. The output of a gate 164 passes to a switch 165 and, inturn, to the gating 160. Intermediate gating including a select up-downcounter 166 and gating 167 producing a reading on counter 168 that isrepresentative of the position of the wheel with respect to theworkpiece at all times. This can be provided as a readout 128.

In the feed pacer mode, the depression of the switch 107 in the controlpanel (FIG. 8) functions in the function generator (FIG. 12) to inhibitthe fast feed decode and medium feed decode shown as at 107a in FIG. 12so that the sequence shift register will function to control the rate ofspeed by the hardness, that is, by the motor current. Thus, the input ofcurrent control in the pacer mode at the left in FIG. 12 passes to amultiplexer or switch 170 which functions as a switch to a summingamplifier 171 which functions to sum the armature current and the analogvoltage dialed into thumb switch 102 corresponding to the desired infeedforce and transmits the difierent to another multiplexer 172 through anacceleration-deceleration limiter 173 and is then converted to pulses bya voltage control oscillator 174. The pulses then pass to the gate 160operating to apply a proportional current to the motor 25. Thus, therotation of the motor 25 that controls the feed is in the pacer modelimited only by the current control which, in turn, is a function of thehardness of the workpieces.

In both modes of operation, the sensing of the contact with theworkpiece to change from rapid traverse to feed is achieved by sensingincrease in motor current. This is designated as points A and B in FIG.9. The circuitry for this control is shown in the bottom portion of FIG.123 wherein the armature current is applied, upon signal of the shiftregister 161 during the last portion of the rapid traverse just prior tocontact, to a sample and holding circuit 175 and is compared in acomparator 176 with an input of a setting 177. Upon increase of thearmature current beyond a predetermined amount caused by contact withthe workpiece, a signal is provided by comparator 176 to the sequenceshift register 161 to cause the register to shift to the next feedportion of the cycle, namely, the fast feed.

As indicated above, provision is made for controlling the rate ofrotation of the workpiece. This incorporates circuitry for calculatingthe S.F.M. in each cycle and for making a comparison to, in turn,initiate a dressing cycle, if required. As shown in FIG. 11, upon thebeginning of each cycle, a signal is provided to a timing logic 176which functions to trigger different signals at appropriate times asrequired and, in turn, to a gate 177, to the counter, the count of whichhas been set by thumbwheel 118 of the control panel. The input of thepreset diameter from thumbwheel switch 116 passes to a counter 178 and amemory 179 that stores the signal, then to a digital to analog converter180 and a comparator 181. The comparator 181 compares the signal fromthe tachometer driven by the work with that of converter 180 to apply avoltage through the line 182 to rotate the motor 13 that drives theworkpiece W at an appropriate R.P.M. that corresponds to the diameter ofthe workpiece and the setting of S.F.M.

At the beginning of each cycle, a cycle counter 185 (FIG. 12B) isinitiated and functions to count infeed cycles. The output of the cyclecounter 185 passes through a gate 186 and a divide counter 187 to Acounter 189a that functions to remember the first cycle time. Secondgate 187' functions to direct the cycle time of subsequent cycles to Bcounter. The setting of the thumbwheel switch 114 into which there hasbeen previously provided a setting of the degree of permissible grindingwheel wear is provided to a divide counter 188 and, in turn, to Bcounter 18% and then to a comparator 190 that compares the cycle timebetween A counter 189a and B counter 18% to produce a signal forinitiating a dress cycle when the counts in B counter are greater thanthe counts in A counter. This provides a signal to a control 191 toinitiate a dressing cycle. Control 191 also zeroes the Parts BetweenDress Cycle counter 192 after the dress cycle has been completed (FIGS.8, 128). More specifically, divide counter 187 can be of the divide by100 type while divide counter 188 can be, for example, of the divide by200 to 300 type and controlled by the setting of switch 114. When thesignals from the divide counters correspond, a dress signal is produced.

Referring further to FIG. 12A, the inputs during work set-up frombuttons 122, 124 are shown as being provided as an analog to themultiplexer 195 and pass on through the circuitry to move the zero pointas determined in the aforementioned description of the cycle.

Operation Fixed Rate Mode Assuming that the operator has set up themachine as heretofore explained and set the electrical zero at theactual zero corresponding to the completion of the finish feed bydepressing the buttons 130 or 132, the machine is then ready foroperation under either the fixed feed rate mode or the pacer feed ratemode.

Assuming that the operator has depressed button 108 corresponding to thefixed feed rate mode, he places a workpiece in the machine operatingCHUCK and DE- CHUCK buttons and the depresses the AUTO and STARTbuttons. The grinding wheel is then moved at the rapid traverse ratetoward the workpiece with the distance traveled up to the beginning ofthe total feed determined by counting the pulses from the encoder. Aspreviously explained, when the number of pulses corresponds to themovement with a predetermined distance of the beginning of total feed(0.100 inch in the example), deceleration occurs for work contact. Whenthe pulses correspond to the number of pulses established by the switch100, a signal is provided to the shift register 161 to, in turn, providea signal so that the grinding wheel will be moved at the medium feedrate set by thumbwheel switch 110. This rate of movement will continueuntil the count from the encoder corresponds to the pulse countestablished by the setting of switch 104. This will, in turn, cause theshift register 161 to initiate finish speed at a rate set by switch 112and for a distance corresponding to the pulses by the setting of theswitch 106.

As previously discussed, during rapid traverse, the system provides adeceleration of the grinding wheel just prior to the beginning of thefast feed and the shift to fast feed is initiated when the current tothe motor 25 during deceleration increases a predetermined amount.

After the completion of the finish feed length, the shift register 161initiates the dwell and the dwell is continued for the number ofrevolutions set by switch 134.

During each portion of the cycle under constant fixed feed rate, themovement of the grinding wheel toward the workpiece is controlled bymonitoring each revolution of the workpiece and utilizing this tocontrol the pulses at each feed rate setting. The rate set in theswitches 102, 110, 112 is the precise movement of the grinding wheeltoward the workpiece. Once set, the feed rates in switches 102, 110 and112 are correct, irrespective of workpiece diameter or change in theS.F.M. settings of switches 116, 118.

Since the feed lengths as established by switches 100, 104, 106determine a predetermined pulse countand the grinding wheel is moved foreach of the settings at the desired number of pulses as read by theencoder, the grinding wheel is moved accurately the desired distancesand the disadvantages of stepper motors in losing pulses at high speeds,as discussed above, are obviated.

Operation Modified Constant Feed or Feed Pacer Mode Assuming that anoperator has set up the machine as heretofore described and depressesthe feed pacer button 107, he may load a part in the same manner asdescribed above. Upon depressing the START and AUTO buttons, theoperation is substantially the same as described above in connectionwith the fixed feed rate mode except in the interval between thebeginning of total feed and the beginning of finish feed. During thisinterval, the current to the motor 25 is monitored so that the motordrives the grinding wheel against the workpiece with the force set inswitch 102. After the completion of the fast feed portion of the feedpacer cycle, the shift register functions to shift the operation to aconstant or fixed rate mode for the finish feed which corresponds to therate set in switch 112 and the distance set in switch106. The finishfeed thus continues in a constant or fixed rate mode for the distanceset therein and then the dwell functions as in the fast rate mode.

On each cycle under feed pacer mode, just prior to the beginning offinish feed, the time for traversing a predetermined distance, indicatedas 0.001 inch in the example, is compared with the time for a newlydressed wheel and when this corresponds to a predetermined percentage asset in switch 114, a dress cycle signal is produced so that the operatorwill then either manually dress the wheel after completion of the cycleor the operation of an automatic dresser, such as in well known in theart, can be initiated.

In each of the modes of operation of the invention, the speed ofrotation of the workpiece is always controlled in accordance with thediameter setting in switch 116 and the surface feed setting of switch118.

Although the invention has been described in connection with a grindingmachine, various features thereof can be utilized in connection withother machine tools. Those features which relate particularly to arotating grinding wheel are, of course, applicable to a rotating machinetool, and those features which relate to movement toward and away from aworkpiece are applicable to both rotating and non-rotating machinetools. Although the application to a grinding machine has been describedin connection with the manual settings on a control panel, it can beunderstood that where mass production of identical parts is being made,numerical or computer control can be provided.

I claim:

1. In a machine wherein a tool and a workpiece are moved relativelytoward and away from each other to perform a work operation on theworkpiece, the combination comprising a first support for the tool,

a second support for the work member,

a rotatable feed member,

one of said supports being connected with said rotat able feed membersuch that upon rotation of said feed member, said one support is movedrelative to the other support,

an electric motor connected to said feed member for rotating the same,

said motor being of the type which produces a torque that isproportional to the current applied thereto,

and an accurate resolution encoder operable to produce a large number ofpulse signals for each revolution of the feed member. 2. The combinationset forth in claim 1 wherein said motor is of the permanent magnet DCtype.

3. The combination set forth in claim 1 wherein said feed membercomprises a feed screw,

said one support which is operatively connected thereto having a nutthereon through which the screw extends,

said feed screw being rotatably supported by longitudinally spacedbearings,

at least some of said bearings having a preload thereon which functionsto prevent rotation of the feed screw upon a load being applied to theone support operatively connected thereto.

4. The combination set forth in claim 3 including means for applying aconstant current to the motor which is sufficient to equal the preloadon the feed screw such that additional current applied to the motor willproduce a rotation of said feed screw proportional to the additionalcurrent.

5. The combination set forth in claim 1 including hydrostatic supportmeans for said movable support.

6. The combination set forth in claim 1 wherein said encoder comprises apulse generator, coupled to the feed member.

7. The combination set forth in claim 6 wherein said pulse generatorcomprises an optical type generator.

8. The combination set forth in claim 6 wherein said pulse generatorproduces pulses on the order of 20,000 pulses per revolution.

9. The combination set forth in claim 1 wherein said encoder is of thetype such that each pulse is produced by movement of the support on theorder of one tenmillionth of an inch.

10. The combination set forth in claim 1 including a pulse generator forproducing a plurality of pulses,

and means for converting said pulses to a voltage and applying them tothe motor.

11. The combination set forth in claim 1 including means for applying apredetermined voltage to said motor to rotate the motor and, in turn,move the feed member and the support connected thereto at apredetermined rate,

means for comparing the pulses received from the encoder to apredetermined count,

and means for terminating the application of voltage to said motor whenthe pulses from the encoder are equal to the predetermined count.

12. The combination set forth in claim 1 including means for monitoringthe current being applied to the motor,

means for comparing said monitored current to a predetermined standard,

and means for controlling the current such that it does not exceed thepredetermined standard.

13. The combination set forth in claim 12 including means for comparingthe pulse count from the encoder to a predetermined standard,

and means for terminating the controlling of current when the pulsecount equals the predetermined standard.

14. The combination set forth in claim 13 including means for applying apredetermined pulse count and a predetermined pulse rate,

means for converting said pulse rate to a voltage proportional to therate and applying the same to the motor,

means for initiating the application of said lastmentioned pulse rate atthe termination of the controlling of the current,

and means for terminating the application of said last-mentioned voltagewhen the pulse count from the encoder equals the predetermined pulsecount.

15. The combination set forth in claim 1 including counter means forcounting the pulses from the encoder and terminating the particularmovement upon reaching a predetemlined count.

16. The combination set forth in claim 1 including means for applying aplurality of pulses, voltage control means for converting said pulses toa count and applying them to the motor, and means for comparing the rateof said pulses from the encoder to a predetermined standard rate andpermitting the passage of pulses therefrom to the voltage control meansonly at a predetermined maximum rate not exceeding said standard.

17. The combination set forth in claim 1 including control means forsaid motor comprising means for establishing a predetermined pulse rateand predetermined number of counts for each of the portions of desiredmovement of the support,

means for converting each said pulse rate to a voltage,

and means for controlling the application of each said voltage to themotor to provide a movement of said one support in each of thepredetermined rates and distances corresponding to the predeterminednumber of counts.

18. The combination set forth in claim 17 wherein said portions ofmovement comprise a total feed length,

a rapid traverse length.

19. The combination set forth in claim 18 wherein the total feed lengthis further divided into fast feed, medium feed and finish feed portions,each of which has means for varying the rate and length thereof.

20. The combination set forth in claim 18 wherein the total feed isdivided into fast feed and finish feed portions,

means for limiting the current applied to the motor to a predeterminedvalue during the fast feed portron,

and means for limiting the duration of said lastmentioned currentapplied to the motor,

the finish feed portion having means for varying the rate and length offeed of pulses to the means for controlling the motor.

21. The combination set forth in claim 20 including means for comparingthe current applied to the motor to a predetermined standard and meansfor limiting the current to the motor such that it does not exceed thepredetermined standard.

22. The combination set forth in claim 21 including means responsive tothe termination of the fast feed portion for supplying a predeterminedrate of pulses during the finish feed portions and means for convertingsaid rate of pulses to a voltage proportional to said rate and applyingit to said motor.

23. The combination set forth in claim 1 including means for measuringthe duration of a predetermined portion of the movement of theworkpiece,

and means responsive to a predetermined change in this duration toproduce a signal.

24. The combination set forth in claim 1 including means for controllingthe speed of the workpiece comprising means manually programmable forthe diameter and S.F.M. of the workpiece and means responsive to saidlast-mentioned means for varying the speed of the workpiece such thatthe workpiece rotates at the predetermined S.F.M.

25. The combination set forth in claim 1 including means responsive to apredetermined increase of current to the motor upon engagement of thetool with the workpiece to cause a signal changing the rate of movementof the grinding wheel relative to the workpiece.

26. The combination set forth in claim 25 wherein said engagement of theworkpiece is operable to cause means for controlling the currentdelivered to the motor to become operable.

27. The combination set forth in claim 1 including means responsive tothe revolutions of the workpiece per unit time for controlling the rateof a series of pulses,

and means for producing a voltage proportional to the rate of the pulsesand applying said voltage to the motor.

28. The combination set forth in claim 1 including means responsive tothe diameter of the workpiece and a predetermined peripheral surfacespeed of the tool with respect to the workpiece for controlling thespeed of rotation of the workpiece to produce said predetermined surfacespeed.

29. The combination set forth in claim 1 including means forperiodically sensing the time interval for movement of the tool relativeto the workpiece through a predetermined distance,

means for comparing said time with a predetermined time interval,

and means for producing a signal when said sensed time interval exceedssaid predetermined time interval.

30. The combination set forth in claim 1 including means manuallyprogrammable for a predetermined desired diameter of the workpiece, apredetermined surface speed per minute and a predetermined number ofrevolutions of the workpiece for rotating the workpiece for apredetermined number of revolutions.

31. The combination set forth in claim 1 including means for sensing thetime required for the removal of a predetermined amount of material fromthe workpiece,

and means for producing a signal when said time deviates from apredetermined standard by a predetermined percentage.

32. The combination set forth in claim 1 including means for measuringand storing the time for removal of a first predetermined portion of theworkpiece,

means thereafter successively measuring the time for removal of anequivalent portion of the workpiece on each successive cycle,

and means for producing a signal when said any of said successive timesexceeds the first-mentioned time by a predetermined percentage.

33. In a grinding machine wherein a rotating grinding wheel and aworkpiece are moved relatively toward and away from each other toperform a work operation on the workpiece, the combination comprising afirst support for the grinding wheel,

a second support for the work member,

a rotatable feed device,

said first support being directly connected with said rotatable feeddevice such that upon rotation of said feed device, said first supportis moved relative to said second support,

an electric motor directly connected to said feed device,

said motor being of the type which produces a torque that isproportional to the current applied thereto,

and an accurate resolution encoder directly connected to the feed memberand operable to produce a plurality of signals of predetermined durationfor each revolution of the feed member.

34. The combination set forth in claim 33 wherein said motor is of thepermanent magnet DC type.

35. The combination set forth in claim 33 wherein said feed membercomprises a feed screw,

said first support which is operatively connected thereto having a nutthereon through which the screw extends,

said feed screw being supported by longitudinally spaced bearings,

at least some of said bearings having a preload thereon which functionsto prevent rotation of the feed screw upon a load being applied to thesupport connected thereto.

36. The combination set forth in claim 33 including means for applying aconstant current to the motor which is sufiicient to equal the preloadon the feed screw such that additional current supplied to the motorwill produce a rotation of said feed screw proportional to theadditional current.

37. The combination set forth in claim 33 including hydrostatic supportmeans for said movable support.

38. The combination set forth in claim 33 wherein said encoder comprisesa pulse generator, coupled to the feed member.

39. The combination set forth in claim 38 wherein said pulse generatorcomprises an optical type generator.

40. The combination set forth in claim 38 wherein said pulse generatorproduces pulses on the order of 20,000 pulses per revolution.

41. The combination set forth in claim 33 wherein said encoder is of thetype such that each pulse is pro duced by movement of the support on theorder of one ten-millionth of an inch.

42. The combination set forth in claim 33 including a pulse generatorfor producing a plurality of pulses,

means for converting said pulses to a voltage applying them to themotor. 43. The combination set forth in claim 42 including means forreducing the voltage to the motor just prior to contact between theworkpiece and the grinding wheel,

means for monitoring the current of the motor during a portion of saidlast-mentioned monitoring,

and means for initiating the last succeeding portion of the cycle whenthe percentage increase in current exceeds a predetermined amount.

44. The combination set forth in claim 33 including means responsive toa predetermined diameter and predetermined speed for maintaining therelative positions of the workpiece and grinding wheel for apredetermined number of revolutions at the completion of the movement ofthe grinding wheel and workpiece relative toward one another.

45. The combination set forth in claim 33 including means forcontrolling the speed of the workpiece comprising means programmable forthe diameter and SFM of the workpiece and means for varying the speed ofthe workpiece such that the workpiece rotates at the predetermined SFM.

46. The combination set forth in claim 33 including means responsive toa predetermined increase of current upon engagement of the grindingwheel with the workpiece to cause a signal changing the rate of movementof the grinding wheel toward the workpiece.

47. The combination set forth in claim 46 wherein said engagement of theworkpiece is operable to cause means for controlling the currentdelivered to the motor to become operable and thereby limit the movementof the grinding wheel toward the workpiece.

48. In a grinding machine wherein a rotating grinding wheel and aworkpiece are moved relatively toward and away from each other toperform a work operation on the workpiece, the combination comprising afirst support for the grinding wheel,

a second support for the work member,

a rotatable feed screw,

said first support being connected with said feed screw such that uponrotation of said feed screw, said first support is moved relative tosaid second support,

said support which is operatively connected to the feed screw having anut thereon through which the screw extends,

said feed screw being supported by longitudinally spaced bearings,

at least some of said bearings having a preload thereon which functionsto prevent rotation of the feed screw upon a load being applied to thesupport connected thereto,

an electric motor connected to said feed screw,

said motor being of the type which produces a torque that isproportional to the current applied thereto,

and an accurate resolution encoder directly connected to the feed screwoperable to produce a plurality of signals of predetermined duration foreach revolution of the feed screw,

means for controlling the movement of said screw and in turn saidworkpiece with respect to the grinding wheel through a plurality ofportions of a cycle,

means for applying a predetermined rate of pulses and a predeterminednumber of pulses for each such portion,

and means for converting each such rate to a voltage and applying it tothe motor,

means responsive to the angular rate ofmovement of the workpiece orcontrolling the rate at which the pulses are converted to a voltage andapplied to the motor,

said encoder functioning to produce pulses corresponding to the movementbetween the workpiece and grinding wheel,

and means for terminating each portion of the cycle when thepredetermined pulse count for each portion equals the pulse count fromthe encoder.

49. The combination set forth in claim 48 wherein said motor is of thepermanent magnet DC type.

50. The combination set forth in claim 48 including means for applying aconstant current to the motor which is sufficient to equal the preloadon the feed screw such that additional current supplied to the motorwill produce a rotation of said feed screw proportional to theadditional current.

51. The combination set forth in claim 48 including hydrostatic supportmeans for said movable support.

52. The combination set forth in claim 48 wherein said encoder comprisesan optical type generator.

53. The combination set forth in claim 52 wherein said encoder producespulses on the order of 20,000 pulses per revolution.

54. The combination set forth in claim 48 wherein said encoder is of thetype such that each pulse is produced by movement of the support on theorder of one ten-millionth of an inch.

55. The combination set forth in claim 48 wherein said portions ofmovement comprise a total feed length,

a rapid traverse length,

the latter being further divided into a total feed length.

56. The combination set forth in claim 55 wherein the total feed lengthis further divided into fast feed, medium feed and finish feed portions,each of which has means for varying the rate and length thereof.

57. In a grinding machine wherein a rotating grinding wheel and aworkpiece are moved relatively toward and away from each other toperform a work operation on the workpiece, the combination comprising,

a first support for the gridnding wheel,

a second support for the work member,

a rotatable feed device,

said first support being directly connected with said feed screw suchthat upon rotation of said feed screw, said first support is movedrelative to said second support,

said support which is operatively connected thereto having a nut thereonthrough which the screw extends,

said feed screw being supported by longitudinally spaced bearings,

at least some of said bearings having a preload thereon which funcitonsto prevent rotation of the feed screw upon a load being applied to thesupport connected thereto,

an electric motor connected to said feed device,

said motor being of the type which produces a torque that isproportional to the current applied thereto,

and an accurate resolution encoder operable to produce a plurality ofsignals of predetermined duration for each revolution of the feed screw,

means for controlling the movement of said screw and, in turn, saidwrkpiece workpiece respect to the grinding wheel through a plurality ofportions of a cycle,

means for applying a substantially constant current to said motor duringone cycle portion for maintaining said workpiece and grinding wheel incontact with a constant force,

said encoder functioning to produce pulses corresponding to the movementof the workpiece and the grinding wheel,

and means for terminating each portion of the cycle when thepredetermined pulse count for each portion equals the pulse count fromthe encoder.

58. The combination set forth in claim 57 wherein said motor is of thepermanent megnet DC type.

59. The combination set forth in claim 57 including means for applying aconstant current to the motor which is sufficient to equal the preloadon the feed screw such that additional current supplied to the motorwill produce a rotation of said feed screw proportional to the current.

60. The combination set forth in claim 57 including hydrostatic supportmeans for said movable support.

61. The combination set forth in claim 57 wherein said pulse generatorcomprises an optical type generator.

62. The combination set forth in claim 61 wherein said pulse generatorproduces pulses on the order of 20,000 pulses per revolution.

63. The combination set forth in claim 57 wherein said encoder is of thetype such that each pulse is produced by movement of the support on theorder of one ten-millionth of an inch.

64. The combination set forth in claim 57 wherein the total feed isdivided into fast feed and finish feed portions,

the fast feed portion controlled by said means for applying asubstantially constant current to the motor,

the finish feed mode having means for varying the rate and length offeed of pulses to the means for controlling the motor.

65. The combination set forth in claim 57 including means forcontrolling the speed of the workpiece comprising measn programmable forthe diameter and SFM of the workpiece and means for varying the speed ofthe workpiece such that the workpiece rotates at the predetermined SFM.

66. The combination set forth in claim 57 including means responsive toa predetermined increase of current upon engagement of the grindingwheel with the workpiece to cause a signal changing the rate of movementof the grinding wheel toward the workpiece.

67. The combination set forth in claim 57 wherein said engagement of theworkpiece is operable to cause means for controlling the currentdelivered to the motor to become operable and thereby limit the movementof the grinding'wheel toward the workpiece.

68. The combination set forth in claim 57 including means for sensingthe time required for the removal of a predetermined amount of materialfrom the workiece,

p and means for producing a signal when said time deviates from apredetermined standard by a predetermined percentage.

69. The combination set forth in claim 57 including means for measuringand storing the time for removal of a first predetermined portion of theworkpiece,

means thereafter successively measuring the time for removal of anequivalent amount of the workpiece on each successive cycle, and meansfor producing a signal when said any of said successive times exceedsthe first-mentioned time by a predetermined percentage. 70. In agrinding machine, the combination comprismg a first support for agrinding wheel, a second support for a workpiece, means for moving saidsupports relative to one another to bring the workpiece and tool intocontact,

means for measuring and storing the time grinding a first workpiece,means for thereafter measuring the time for grinding a predeterminedequivalent portion of subsequent workpieces,

and means for producing a dressing signal when the time for saidsubsequent grinding exceeds the first mentioned stored time by apredetermined precentage.

71. In a machine tool wherein a tool and a workpiece are movedrelatively toward and away from each other to perform a work operationon the workpiece, the combination comprising a first support for thetool,

a second support for the workpiece,

a rotatable feed device,

one of said supports being connected with said rotatable feed device sothat upon rotation of said feed device said support is moved relative tothe other support,

and an electric motor connected to the feed device,

means for applying a predetermined voltage to the motor just prior tocontact with the workpiece so that the motor operates at constantcurrent,

means for monitoring said current,

and means for producing a work contact signal when the increase incurrent due to contact between the workpiece and tool increases by apredetermined amount.

1. In a machine wherein a tool and a workpiece are moved relativelytoward and away from each other to perform a work operation on theworkpiece, the combination comprising a first support for the tool, asecond support for the work member, a rotatable feed member, one of saidsupports being connected with said rotatable feed member such that uponrotation of said feed member, said one support is moved relative to theother support, an electric motor connected to said feed member forrotating the same, said motor being of the type which produces a torquethat is proportional to the current applied thereto, and an accurateresolution encoder operable to produce a large number of pulse signalsfor each revolution of the feed member.
 2. The combination set forth inclaim 1 wherein said motor is of the permanent magnet DC type.
 3. Thecombination set forth in claim 1 wherein said feed member comprises afeed screw, said one support which is operatively connected theretohaving a nut thereon through which the screw extends, said feed screwbeing rotatably supported by longitudinally spaced bearings, at leastsome of said bearings having a preload thereon which functions toprevent rotation of the feed screw upon a load being applied to the onesupport operatively connected thereto.
 4. The combination set forth inclaim 3 including means for applying a constant current to the motorwhich is sufficient to equal the preload on the feed screw such thatadditional current applied to the motor will produce a rotation of saidfeed screw proportional to the additional current.
 5. The combinationset forth in claim 1 including hydrostatic support means for saidmovable support.
 6. The combination set forth in claim 1 wherein saidencoder comprises a pulse generator, coupled to the feed member.
 7. Thecombination set forth in claim 6 wherein said pulse generator comprisesan optical type generator.
 8. The combination set forth in claim 6wherein said pulse generator produces pulses on the order of 20,000pulses per revolution.
 9. The combination set forth in claim 1 whereinsaid encoder is of the type such that each pulse is produced by movementof the support on the order of one ten-millionth of an inch.
 10. Thecombination set forth in claim 1 including a pulse generator forproducing a plurality of pulses, and means for converting said pulses toa voltage and applying them to the motor.
 11. The combination set forthin claim 1 including means for applying a predetermined voltage to saidmotor to rotate the motor and, in turn, move the feed member and thesupport connected thereto at a predetermined rate, means for comparingthe pulses received from the encoder to a predetermined count, and meansfor terminating the application of voltage to said motor when the pulsesfrom the encoder are equal to the predetermined count.
 12. Thecombination set forth in claim 1 including means for monitoring thecurrent being applied to the motor, means for comparing said monitoredcurrent to a predetermined standard, and means for controlling thecurrent such that it does not exceed the predetermined standard.
 13. Thecombination set forth in claim 12 including means for comparing thepulse count from the encoder to a predetermined standard, and means forterminating the controlling of current when the pulse count equals thepredetermined standard.
 14. The combination set forth in claim 13including means for applying a predetermined pulse count and apredetermined pulse rate, means for converting said pulse rate to avoltage proportional to the rate and applying the same to the motor,means for initiating the application of said lastmentioned pulse rate atthe termination of the controlling of the current, and means forterminating the application of said last-mentioned voltage when thepulse count from the encoder equals the predetermined pulse count. 15.The combination set forth in claim 1 including counter means forcounting the pulses from the encoder and terminating the particularmovement upon reaching a predetermined count.
 16. The combination setforth in claim 1 including means for applying a plurality of pulses,voltage control means for converting said pulses to a count and applyingthem to the motor, and means for comparing the rate of said pulses fromthe encoder to a predetermined standard rate and permitting the passageof pulses therefrom to the voltage control means only at a predeterminedmaximum rate not exceeding said standard.
 17. The combination set forthin claim 1 including control means for said motor comprising means forestablishing a predetermined pulse rate and predetermined number ofcounts for each of the portions of desired movement of the support,means for converting each said pulse rate to a voltage, and means forcontrolling the application of each said voltage to the motor to providea movement of said one support in each of the predetermined rates anddistances corresponding to the predetermined number of counts.
 18. Thecombination set forth in claim 17 wherein said portions of movementcomprise a total feed length, a rapid traverse length.
 19. Thecombination set forth in claim 18 wherein the total feed length isfurther divided into fast feed, medium feed and finish feed portions,each of which has means for varying the rate and length thereof.
 20. Thecombination set forth in claim 18 wherein the total feed is divided intofast feed and finish feed portions, means for limiting the currentapplied to the motor to a predetermined value during the fast feedportion, and means for limiting the duration of said last-mentionedcurrent applied to the motor, the finish feed portion having means forvarying the rate and length of feed of pulses to the means forcontrolling the motor.
 21. The combination set forth in claim 20including means for comparing the current applied to the motor to apredetermined standard and means for limiting the current to the motorsuch that it does not exceed the predetermined standard.
 22. Thecombination set forth in claim 21 including means responsive to thetermination of the fast feed portion for supplying a predetermined rateof pulses during the finish feed portions and means for converting saidrate of pulses to a voltage proportional to said rate and applying it tosaid motor.
 23. The combination set forth in claim 1 including means formeasuring the duration of a predetermined portion of the movement of theworkpiece, and means responsive to a predetermined change in thisduration to produce a signal.
 24. The combination set forth in claim 1including means for controlling the speed of the workpiece comprisingmeans manually programmable for the diameter and S.F.M. of the workpieceand means responsive to said last-mentioned means for varying the speedof the workpiece such that the workpiece rotates at the predeterminedS.F.M.
 25. The combination set forth in claim 1 including meansresponsive to a predetermined increase of current to the motor uponengagement of the tool with the workpiece to cause a signal changing therate of movement of the grinding wheel relative to the workpiece. 26.The combination set forth in claim 25 wherein said engagement of theworkpiece is operable to cause means for controlling the currentdelivered to the motor to become operable.
 27. The combination set forthin claim 1 including means responsive to the revolutions of theworkpiece per unit time for controlling the rate of a series of pulses,and means for producing a voltage proportional to the rate of the pulsesand applying said voltage to the motor.
 28. The combination set forth inclaim 1 including means responsive to the diameter of the workpiece anda predetermined peripheral surface speed of the tool with respect to theworkpiece for controlling the speed of rotation of the workpiece toproduce said predetermined surface speed.
 29. The combination set forthin claim 1 including means for periodically sensing the time intervalfor movement of the tool relative to the workpiece through apredetermined distance, means for comparing said time with apredetermined time interval, and means for producing a signal when saidsensed time interval exceeds said predetermined time interval.
 30. Thecombination set forth in claim 1 including means manually programmablefor a predetermined desired diameter of the workpiece, a predeterminedsurface speed per minute and a predetermined number of revolutions ofthe workpiece for rotating the workpiece for a predetermined number ofrevolutions.
 31. The combination set forth in claim 1 including meansfor sensing the time required for the removal of a predetermined amountof material from the workpiece, and means for producing a signal whensaid time deviates from a predetermined standard by a predeterminedpercentage.
 32. The combination set forth in claim 1 including means formeasuring and storing the time for removal of a first predeterminedportion of the workpiece, means thereafter successively measuring thetime for removal of an equivalent portion of the workpiece on eachsuccessive cycle, and means for producing a signal when said any of saidsuccessive times exceeds the first-mentioned time by a predeterminedpercentage.
 33. In a grinding machine wherein a rotating grinding whEeland a workpiece are moved relatively toward and away from each other toperform a work operation on the workpiece, the combination comprising afirst support for the grinding wheel, a second support for the workmember, a rotatable feed device, said first support being directlyconnected with said rotatable feed device such that upon rotation ofsaid feed device, said first support is moved relative to said secondsupport, an electric motor directly connected to said feed device, saidmotor being of the type which produces a torque that is proportional tothe current applied thereto, and an accurate resolution encoder directlyconnected to the feed member and operable to produce a plurality ofsignals of predetermined duration for each revolution of the feedmember.
 34. The combination set forth in claim 33 wherein said motor isof the permanent magnet DC type.
 35. The combination set forth in claim33 wherein said feed member comprises a feed screw, said first supportwhich is operatively connected thereto having a nut thereon throughwhich the screw extends, said feed screw being supported bylongitudinally spaced bearings, at least some of said bearings having apreload thereon which functions to prevent rotation of the feed screwupon a load being applied to the support connected thereto.
 36. Thecombination set forth in claim 33 including means for applying aconstant current to the motor which is sufficient to equal the preloadon the feed screw such that additional current supplied to the motorwill produce a rotation of said feed screw proportional to theadditional current.
 37. The combination set forth in claim 33 includinghydrostatic support means for said movable support.
 38. The combinationset forth in claim 33 wherein said encoder comprises a pulse generator,coupled to the feed member.
 39. The combination set forth in claim 38wherein said pulse generator comprises an optical type generator. 40.The combination set forth in claim 38 wherein said pulse generatorproduces pulses on the order of 20,000 pulses per revolution.
 41. Thecombination set forth in claim 33 wherein said encoder is of the typesuch that each pulse is produced by movement of the support on the orderof one ten-millionth of an inch.
 42. The combination set forth in claim33 including a pulse generator for producing a plurality of pulses,means for converting said pulses to a voltage applying them to themotor.
 43. The combination set forth in claim 42 including means forreducing the voltage to the motor just prior to contact between theworkpiece and the grinding wheel, means for monitoring the current ofthe motor during a portion of said last-mentioned monitoring, and meansfor initiating the last succeeding portion of the cycle when thepercentage increase in current exceeds a predetermined amount.
 44. Thecombination set forth in claim 33 including means responsive to apredetermined diameter and predetermined speed for maintaining therelative positions of the workpiece and grinding wheel for apredetermined number of revolutions at the completion of the movement ofthe grinding wheel and workpiece relative toward one another.
 45. Thecombination set forth in claim 33 including means for controlling thespeed of the workpiece comprising means programmable for the diameterand SFM of the workpiece and means for varying the speed of theworkpiece such that the workpiece rotates at the predetermined SFM. 46.The combination set forth in claim 33 including means responsive to apredetermined increase of current upon engagement of the grinding wheelwith the workpiece to cause a signal changing the rate of movement ofthe grinding wheel toward the workpiece.
 47. The combination set forthin claim 46 wherein said engagement of the workpiece is operable tocause means for controlling the current delivered to the motor to becomeoperable and thereby limit the movement of The grinding wheel toward theworkpiece.
 48. In a grinding machine wherein a rotating grinding wheeland a workpiece are moved relatively toward and away from each other toperform a work operation on the workpiece, the combination comprising afirst support for the grinding wheel, a second support for the workmember, a rotatable feed screw, said first support being connected withsaid feed screw such that upon rotation of said feed screw, said firstsupport is moved relative to said second support, said support which isoperatively connected to the feed screw having a nut thereon throughwhich the screw extends, said feed screw being supported bylongitudinally spaced bearings, at least some of said bearings having apreload thereon which functions to prevent rotation of the feed screwupon a load being applied to the support connected thereto, an electricmotor connected to said feed screw, said motor being of the type whichproduces a torque that is proportional to the current applied thereto,and an accurate resolution encoder directly connected to the feed screwoperable to produce a plurality of signals of predetermined duration foreach revolution of the feed screw, means for controlling the movement ofsaid screw and in turn said workpiece with respect to the grinding wheelthrough a plurality of portions of a cycle, means for applying apredetermined rate of pulses and a predetermined number of pulses foreach such portion, and means for converting each such rate to a voltageand applying it to the motor, means responsive to the angular rate ofmovement of the workpiece or controlling the rate at which the pulsesare converted to a voltage and applied to the motor, said encoderfunctioning to produce pulses corresponding to the movement between theworkpiece and grinding wheel, and means for terminating each portion ofthe cycle when the predetermined pulse count for each portion equals thepulse count from the encoder.
 49. The combination set forth in claim 48wherein said motor is of the permanent magnet DC type.
 50. Thecombination set forth in claim 48 including means for applying aconstant current to the motor which is sufficient to equal the preloadon the feed screw such that additional current supplied to the motorwill produce a rotation of said feed screw proportional to theadditional current.
 51. The combination set forth in claim 48 includinghydrostatic support means for said movable support.
 52. The combinationset forth in claim 48 wherein said encoder comprises an optical typegenerator.
 53. The combination set forth in claim 52 wherein saidencoder produces pulses on the order of 20,000 pulses per revolution.54. The combination set forth in claim 48 wherein said encoder is of thetype such that each pulse is produced by movement of the support on theorder of one ten-millionth of an inch.
 55. The combination set forth inclaim 48 wherein said portions of movement comprise a total feed length,a rapid traverse length, the latter being further divided into a totalfeed length.
 56. The combination set forth in claim 55 wherein the totalfeed length is further divided into fast feed, medium feed and finishfeed portions, each of which has means for varying the rate and lengththereof.
 57. In a grinding machine wherein a rotating grinding wheel anda workpiece are moved relatively toward and away from each other toperform a work operation on the workpiece, the combination comprising, afirst support for the gridnding wheel, a second support for the workmember, a rotatable feed device, said first support being directlyconnected with said feed screw such that upon rotation of said feedscrew, said first support is moved relative to said second support, saidsupport which is operatively connected thereto having a nut thereonthrough which the screw extends, said feed screw being supported bylongitudinally spaced bearings, at least some of said bearings having apreload thereon which funcitons to prevent rotation of the feed screwupon a load being applied to the support connected thereto, an electricmotor connected to said feed device, said motor being of the type whichproduces a torque that is proportional to the current applied thereto,and an accurate resolution encoder operable to produce a plurality ofsignals of predetermined duration for each revolution of the feed screw,means for controlling the movement of said screw and, in turn, saidwrkpiece workpiece respect to the grinding wheel through a plurality ofportions of a cycle, means for applying a substantially constant currentto said motor during one cycle portion for maintaining said workpieceand grinding wheel in contact with a constant force, said encoderfunctioning to produce pulses corresponding to the movement of theworkpiece and the grinding wheel, and means for terminating each portionof the cycle when the predetermined pulse count for each portion equalsthe pulse count from the encoder.
 58. The combination set forth in claim57 wherein said motor is of the permanent megnet DC type.
 59. Thecombination set forth in claim 57 including means for applying aconstant current to the motor which is sufficient to equal the preloadon the feed screw such that additional current supplied to the motorwill produce a rotation of said feed screw proportional to the current.60. The combination set forth in claim 57 including hydrostatic supportmeans for said movable support.
 61. The combination set forth in claim57 wherein said pulse generator comprises an optical type generator. 62.The combination set forth in claim 61 wherein said pulse generatorproduces pulses on the order of 20,000 pulses per revolution.
 63. Thecombination set forth in claim 57 wherein said encoder is of the typesuch that each pulse is produced by movement of the support on the orderof one ten-millionth of an inch.
 64. The combination set forth in claim57 wherein the total feed is divided into fast feed and finish feedporrions, the fast feed portion controlled by said means for applying asubstantially constant current to the motor, the finish feed mode havingmeans for varying the rate and length of feed of pulses to the means forcontrolling the motor.
 65. The combination set forth in claim 57including means for controlling the speed of the workpiece comprisingmeasn programmable for the diameter and SFM of the workpiece and meansfor varying the speed of the workpiece such that the workpiece rotatesat the predetermined SFM.
 66. The combination set forth in claim 57including means responsive to a predetermined increase of current uponengagement of the grinding wheel with the workpiece to cause a signalchanging the rate of movement of the grinding wheel toward theworkpiece.
 67. The combination set forth in claim 57 wherein saidengagement of the workpiece is operable to cause means for controllingthe current delivered to the motor to become operable and thereby limitthe movement of the grinding wheel toward the workpiece.
 68. Thecombination set forth in claim 57 including means for sensing the timerequired for the removal of a predetermined amount of material from theworkpiece, and means for producing a signal when said time deviates froma predetermined standard by a predetermined percentage.
 69. Thecombination set forth in claim 57 including means for measuring andstoring the time for removal of a first predetermined portion of theworkpiece, means thereafter successively measuring the time for removalof an equivalent amount of the workpiece on each successive cycle, andmeans for producing a signal when said any of said successive timesexceeds the first-mentioned time by a predetermined percentage.
 70. In agrinding machine, the combination comprising a first suppOrt for agrinding wheel, a second support for a workpiece, means for moving saidsupports relative to one another to bring the workpiece and tool intocontact, means for measuring and storing the time grinding a firstworkpiece, means for thereafter measuring the time for grinding apredetermined equivalent portion of subsequent workpieces, and means forproducing a dressing signal when the time for said subsequent grindingexceeds the first mentioned stored time by a predetermined precentage.71. In a machine tool wherein a tool and a workpiece are movedrelatively toward and away from each other to perform a work operationon the workpiece, the combination comprising a first support for thetool, a second support for the workpiece, a rotatable feed device, oneof said supports being connected with said rotatable feed device so thatupon rotation of said feed device said support is moved relative to theother support, and an electric motor connected to the feed device, meansfor applying a predetermined voltage to the motor just prior to contactwith the workpiece so that the motor operates at constant current, meansfor monitoring said current, and means for producing a work contactsignal when the increase in current due to contact between the workpieceand tool increases by a predetermined amount.